Holographic display apparatus for providing expanded viewing window

ABSTRACT

A holographic display apparatus for providing an expanded viewing window includes a spatial filter configured to separate a plurality of holographic images generated by the hologram pattern displayed on the spatial light modulator from a plurality of lattice spots generated by a physical structure of the spatial light modulator. The spatial filter includes a plurality of color filters or a plurality of dichroic mirrors separating a first color image, a second color image, and a third color image from a first color lattice spot, a second color lattice spot, and a third color lattice spot.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.16/034,931, filed on Jul. 13, 2018, which claims priority from KoreanPatent Application No. 10-2018-0019523, filed on Feb. 19, 2018, in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND 1. Field

Apparatuses consistent with exemplary embodiments relate to aholographic display apparatus, and more particularly to, a holographicdisplay apparatus that provides an expanded viewing window whenreproducing a holographic image via an off-axis technique.

2. Description of the Related Art

Methods such as glasses-type methods and non-glasses-type methods arewidely used for realizing 3D images. Examples of glasses-type methodsinclude deflected glasses-type methods and shutter glasses-type methods,and examples of non-glasses-type methods include lenticular methods andparallax barrier methods. When these methods are used, there is a limitto the number of viewpoints that may be implemented due to binocularparallax. Also, these methods make the viewers feel tired due to thedifference between the depth perceived by the brain and the focus of theeyes.

Recently, holographic 3D image display methods, which provide fullparallax and are capable of making the depth perceived by the brainconsistent with the focus of the eyes, have been gradually put topractical use. According to such a holographic display technique, whenlight is irradiated onto a hologram pattern having recorded thereon aninterference pattern obtained by interference between reference lightand object light reflected from an original object, the light isdiffracted and an image of the original object is reproduced. When acurrently commercialized holographic display technique is used, acomputer-generated hologram (CGH), rather than a hologram patternobtained by directly exposing an original object to light, is providedto a spatial light modulator as an electrical signal. The spatial lightmodulator then forms a hologram pattern and diffracts light according tothe input CGH signal, thereby generating a 3D image.

SUMMARY

According to an aspect of an exemplary embodiment, a holographic displayapparatus includes a light source configured to provide light; a spatiallight modulator configured to display a hologram pattern for reproducinga holographic image by modulating incident light; and a spatial filterconfigured to separate a plurality of holographic images generated bythe hologram pattern displayed on the spatial light modulator from aplurality of lattice spots generated by a physical structure of thespatial light modulator, wherein each of the plurality of holographicimages includes a first color image, a second color image, and a thirdcolor image formed at different positions, wherein each of the pluralityof lattice spots includes a first color lattice spot, a second colorlattice spot, and a third color lattice spot formed at differentpositions, and wherein the spatial filter includes a plurality of colorfilters or a plurality of dichroic mirrors configured to separate thefirst color image, the second color image, and the third color imagefrom the first color lattice spot, the second color lattice spot, andthe third color lattice spot.

The spatial filter may include a first pinhole transmitting aholographic image generated by a 0^(th) order diffraction in the spatiallight modulator, and a plurality of second pinholes respectivelytransmitting a plurality of high order holographic images generated by a±1^(st) or higher order diffraction in the spatial light modulator.

The first pinhole may be configured to transmit the first color image,the second color image, and the third color image.

Each of the plurality of second pinholes may comprise the plurality ofcolor filters.

Each of the plurality of second pinholes may include a first region onwhich the first color image is incident, a second region on which thefirst color image and the second color image are incident, a thirdregion on which the second color image is incident, a fourth region onwhich the first color image, the second color image and the third colorimage are incident, a fifth region on which the second color image andthe third color image are incident, and a sixth region on which thethird color image is incident.

The plurality of color filters may include: a first color filterdisposed in the first region and configured to transmit the first colorimage; a second color filter disposed in the second region andconfigured to transmit the first color image and the second color image;a third color filter disposed in the third region and configured totransmit the second color image; a fourth color filter disposed in thefourth region and configured to transmit the first color image, thesecond color image, and the third color image; a fifth color filterdisposed in the fifth region and configured to transmit the second colorimage and the third color image; and a sixth color filter disposed inthe sixth region and configured to transmit the third color image.

A distance between the first color filter and the first pinhole may beless than a distance between the sixth color filter and the firstpinhole.

The spatial filter may include a first reflective surface reflecting aholographic image generated by a 0th order diffraction in the spatiallight modulator and a plurality of second reflective surfacesrespectively reflecting a plurality of high order holographic imagesgenerated by a ±1st order or higher diffraction in the spatial lightmodulator.

The first reflective surface may be configured to reflect the firstcolor image, the second color image, and the third color image of theholographic image generated by the 0^(th) order diffraction.

Each of the plurality of second reflective surfaces may include theplurality of dichroic mirrors.

Each of the plurality of second reflective surfaces may include a firstregion on which the first color image is incident, a second region onwhich the first color image and the second color image are incident, athird region on which the second color image is incident, a fourthregion on which the first color image, the second color image and thethird color image are incident, a fifth region on which the second colorimage and the third color image are incident, and a sixth region onwhich the third color image is incident.

The plurality of dichroic mirrors may include a first dichroic mirrordisposed in the first region and configured to reflect the first colorimage; a second dichroic mirror disposed in the second region andconfigured to reflect the first color image and the second color image;a third dichroic mirror disposed in the third region and configured toreflect the second color image; a fourth dichroic mirror disposed in thefourth region and configured to reflect the first color image, thesecond color image, and the third color image; a fifth dichroic mirrordisposed in the fifth region and configured to reflect the second colorimage and the third color image; and a sixth dichroic mirror disposed inthe sixth region and configured to reflect the third color image.

The holographic display apparatus may further include a first lensdisposed between the spatial light modulator and the spatial filter; anda second lens configured to focus the plurality of holographic imagesseparated by the spatial filter.

The spatial filter may include a first spatial filter disposed at aposition at which the first color image is focused by the first lens; asecond spatial filter disposed at a position at which the second colorimage is focused by the first lens; and a third spatial filter disposedat a position at which the third color image is focused by the firstlens.

The first spatial filter may include a plurality of first color blockingfilters disposed at positions corresponding to the first color latticespots and configured to block light of a first color and to transmitlight of the second color and the third color, wherein the secondspatial filter includes a plurality of second color blocking filtersdisposed at positions corresponding to the second color lattice spotsand configured to block light of a second color and to transmit light ofthe first color and the third color, and wherein the third spatialfilter includes a plurality of third color blocking filters disposed atpositions corresponding to the third color lattice spots and configuredto block light of a third color and to transmit light of the first colorand the second color.

Remaining regions of the first through third spatial filters in whichthe first through third color filters are not disposed may include atransparent material.

The first spatial filter may include a plurality of first color blockingfilters further disposed at positions corresponding to complex conjugateimages of the first color image, wherein the second spatial filterincludes a plurality of second color blocking filters further disposedat positions corresponding to complex conjugate images of the secondcolor image, and wherein the third spatial filter includes a pluralityof third color blocking filters further disposed at positionscorresponding to complex conjugate image of the third color image.

The first spatial filter may include a plurality of first dichroicmirrors disposed at positions corresponding to the first color imagesand configured to reflect light of the first color and to transmit lightof the second color and the third color, wherein the second spatialfilter includes a plurality of second dichroic mirrors disposed atpositions corresponding to the second color images and configured toreflect light of the second color and to transmit light of the firstcolor and the third color a, and wherein the third spatial filterincludes a plurality of third dichroic mirrors disposed at positionscorresponding to the third color images and configured to reflect lightof the third color and to transmit light of the first color and thethird color.

Remaining regions of the first to third spatial filters in which thefirst to third dichroic mirrors are not disposed may include atransparent material.

The spatial filter may have a hemispheric or paraboloid shape.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other exemplary aspects and advantages will become apparentand more readily appreciated from the following description of exemplaryembodiments, taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram schematically illustrating a configuration of aholographic display apparatus according to an exemplary embodiment;

FIG. 2 illustrates a periodic diffraction pattern displayed on a spatiallight modulator to reproduce a holographic image via an off-axistechnique according to an exemplary embodiment;

FIG. 3 illustrates positions of a plurality of holographic images and aplurality of lattice spots via an off-axis technique according to anexemplary embodiment;

FIG. 4 illustrates positions of a plurality of holographic images foreach color reproduced via an off-axis technique and a plurality oflattice spots for each color according to an exemplary embodiment;

FIG. 5 illustrates positions and shapes of a plurality of pinholes of aspatial filter of the holographic display apparatus shown in FIG. 1according to an exemplary embodiment;

FIG. 6 illustrates an arrangement of a plurality of color filtersdisposed in a second pinhole of a spatial filter of the holographicdisplay apparatus shown in FIG. 1 according to an exemplary embodiment;

FIG. 7 is a configuration diagram schematically showing a configurationof a holographic display apparatus according to another exemplaryembodiment;

FIGS. 8A to 8C illustrate configurations of first to third spatialfilters of the holographic display apparatus shown in FIG. 7,respectively, according to an exemplary embodiment;

FIGS. 9A to 9C illustrate different configurations of the first to thirdspatial filters of the holographic display apparatus shown in FIG. 7,respectively, according to an exemplary embodiment;

FIG. 10 is a schematic diagram showing a configuration of a holographicdisplay apparatus according to another exemplary embodiment;

FIG. 11 is a schematic diagram showing a configuration of a holographicdisplay apparatus according to another exemplary embodiment;

FIG. 12 illustrates positions and shapes of a plurality of reflectivesurfaces of a spatial filter of the holographic display apparatus shownin FIG. 11, according to an exemplary embodiment;

FIG. 13 illustrates an arrangement of a plurality of dichroic mirrorsdisposed on a second reflective surface in a spatial filter of theholographic display apparatus shown in FIG. 11 according to an exemplaryembodiment;

FIG. 14 is a schematic diagram showing a configuration of a holographicdisplay apparatus according to another exemplary embodiment; and

FIGS. 15A to 15C illustrate configurations of the first to third spatialfilters of the holographic display apparatus of FIG. 14, respectively,according to an exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, with reference to the accompanying drawings, a holographicdisplay apparatus for providing an expanded viewing window will bedescribed in detail. Like reference numerals refer to like elementsthroughout, and in the drawings, sizes of elements may be exaggeratedfor clarity and convenience of explanation. The embodiments describedbelow are merely exemplary, and various modifications may be possiblefrom the embodiments. In a layer structure described below, anexpression “above” or “on” may include not only “immediately on in acontact manner” but also “on in a non-contact manner”. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

FIG. 1 is a diagram schematically illustrating a configuration of aholographic display apparatus 100 according to an exemplary embodiment.Referring to FIG. 1, the holographic display apparatus 100 according toan exemplary embodiment may include a light source 110 for providinglight, a spatial light modulator 120 for forming a hologram pattern formodulating incident light to reproduce a holographic image, and anoptical system 130 for focusing the holographic image onto a space.

The light source 110 may include a laser providing light having a highcoherency to the spatial light modulator 120. However, if the lightincident on the spatial light modulator 120 has at least a certain levelof spatial coherence, since the light may be diffracted and modulated bythe spatial light modulator 120, a light-emitting diode (LED) may beused as the light source 110. In addition to the LED, any other lightsource may be used as long as light having spatial coherence is emitted.Although one light source 110 is illustrated in FIG. 1 for convenienceof description, the light source 110 may include an array of a pluralityof lasers or LEDs.

The spatial light modulator 120 may form a hologram pattern fordiffracting and modulating the incident light, according to a hologramdata signal provided by an image processor (not shown). The spatiallight modulator 120 may comprise any one of a phase modulator forperforming phase modulation, an amplitude modulator for performingamplitude modulation, and a complex modulator performing both phasemodulation and amplitude modulation. Although the spatial lightmodulator 120 of FIG. 1 is a transmissive spatial light modulator, areflective spatial light modulator may alternately be used. Thetransmissive spatial light modulator may comprise, for example, asemiconductor modulator based on a compound semiconductor such asgallium arsenide (GaAs), or a liquid crystal device (LCD). Thereflective spatial light modulator may comprise, for example, a digitalmicromirror device (DMD), liquid crystal on silicon (LCoS) technology,or a semiconductor modulator.

The optical system 130 focuses light diffracted and modulated by thespatial light modulator 120 so that a holographic image is reproduced ona predetermined focal plane. To this end, in order to focus incidentlight onto a focal plane, the optical system 130 may include a firstlens 131 and a second lens 132. Also, the optical system 130 may beconfigured to expand a viewing window, i.e., a location at which theholographic image may be observed. To this end, the optical system 130may further include a spatial filter 133 configured to allow a pluralityof holographic images generated by a 0^(th) order or higher diffraction,due to the hologram pattern displayed on the spatial light modulator120, to be transmitted therethrough. The first lens 131 may focus animage reproduced by the spatial light modulator 120 onto the spatialfilter 133. The second lens 132 may focus the holographic imageseparated by the spatial filter 133 onto a focal plane of the opticalsystem 130.

An operation of the holographic display apparatus 100 will now bedescribed below. The image processor (not shown) may generate a hologramdata signal and provide the hologram data signal to the spatial lightmodulator 120. The hologram data signal may be a computer-generatedhologram (CGH) signal computed to reproduce a target holographic image.The image processor may generate the hologram data signal according to aholographic image to be reproduced. The spatial light modulator 120 mayform a hologram pattern on a surface of the spatial light modulator 120according to the hologram data signal provided from the image processor.A principle of the spatial light modulator 120 forming the hologrampattern may be the same as a principle of, for example, a display paneldisplaying an image. For example, the hologram pattern may be displayedon the spatial light modulator 120 as an interference pattern includinginformation regarding the holographic image to be reproduced.

Simultaneously, the light source 110 may provide the light to thespatial light modulator 120. The light incident on the spatial lightmodulator 120 may be diffracted and interfered with by the hologrampattern formed by the spatial light modulator 120. Then, the diffractedand interfered light may be focused on the focal plane of the opticalsystem 130, and a three-dimensional holographic image may be reproducedat a predetermined space in front of the spatial light modulator 120.The shape and depth of the holographic image to be reproduced may bedetermined according to the hologram pattern formed by the spatial lightmodulator 120.

A spatial light modulator 120, typically used to perform one of a phasemodulation and an amplitude modulation, comprises an array of aplurality of pixels, and thus the array of the plurality of pixelsfunctions as a lattice. Thus, the incident light may be diffracted andinterfered with not only by the hologram pattern formed by the spatiallight modulator 120 but also by the pixel lattice of the spatial lightmodulator 120. Also, some of the incident light may not be diffracted bythe hologram pattern, but may be transmitted without diffraction. As aresult, a plurality of lattice spots may appear on the focal plane ofthe optical system 130 on which the holographic image is focused. Theplurality of lattice spots may function as image noise that degrades thequality of the resultant holographic image and makes it uncomfortablefor an observer to observe the holographic image.

To prevent the plurality of lattice spots from being seen by theobserver, the holographic image may be reproduced via an off-axistechnique so that a spot of the holographic image is reproduced whileavoiding the plurality of lattice spots. The plurality of lattice spotsare generated due to the internal structure of the spatial lightmodulator 120 and are unrelated to the hologram pattern, and thus thepositions of the plurality of lattice spots are always fixed. However, aspot position of the holographic image is determined according to thehologram pattern, and thus the hologram pattern may be formed such thatthe holographic image is reproduced at a position at which the pluralityof lattice spots are not present.

According to the off-axis technique, the spatial light modulator 120 mayalso form a periodic diffraction pattern for adjusting the reproductionposition of the holographic image to be reproduced, together with thehologram pattern including information of the holographic image. To thisend, the image processor may generate a diffraction pattern data signalas well as the hologram data signal and provide both signals to thespatial light modulator 120. Since a traveling direction of the incidentlight provided from the light source 110 is deviated by the periodicdiffraction pattern displayed on the spatial light modulator 120, thereproduction position of the holographic image may be deviated from thelattice spot. A degree to which the reproduction position of theholographic image is shifted may be determined according to a period ofthe diffraction pattern.

FIG. 2 illustrates a periodic diffraction pattern P displayed on thespatial light modulator 120 to reproduce a holographic image via anoff-axis technique according to an exemplary embodiment. In FIG. 2,although only the diffraction pattern P is shown for convenience, thespatial light modulator 120 may simultaneously display a hologrampattern for reproducing a holographic image together with thediffraction pattern P. As shown in FIG. 2, the diffraction pattern P hasa period ∧x in an x-direction and a period ∧y in a y-direction. In thisregard, the period ∧x in the x-direction is an interval betweenrespective lattice lines constituting the diffraction pattern P, and theperiod ∧y in the y-direction between the lattice lines constituting thediffraction pattern P. A degree to which a reproduction position of theholographic image deviates from a lattice spot may be determinedaccording to the periods ∧x and ∧y of the diffraction pattern P.

FIG. 3 illustrates positions of a plurality of holographic images and aplurality of lattice spots N1 according to an off-axis technique,according to an exemplary embodiment. Referring to FIG. 3, one latticespot N0 at the center is generated due to a 0^(th) order diffraction bya physical structure (i.e. a pixel lattice) inside the spatial lightmodulator 120, and the plurality of lattice spots N1 at the periphery ofthe lattice spot N0 are generated due to ±1^(st) order diffraction bythe pixel lattice of the spatial light modulator 120. In FIG. 3, animage denoted by L₀₀ is a holographic image generated due to 0^(th)order diffraction by the hologram pattern formed by the spatial lightmodulator 120, images denoted by L₀₁, L⁻⁰¹, L₁₀ and L⁻¹⁰ are holographicimages generated due to ±1^(st) order diffraction by the hologrampattern formed by the spatial light modulator 120. When a hologrampattern is formed without taking the lattice spots N0 and N1 intoconsideration, the lattice spots N0 and N1 will be positioned at spotcenters of the reproduced holographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀, andL⁻¹⁰. As a result, a noise image of the lattice spots N0 and N1 and theholographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀, and L⁻¹⁰ may be seen together.

Therefore, the holographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀, and L⁻¹⁰ may beformed to avoid the lattice spots N0 and N1 so as to prevent the latticespots N0 and N1 from being seen by the observer. For example, as shownin FIG. 3, reproduction positions of the holographic image L₀₀, L₀₁,L⁻⁰¹, L₁₀, and L⁻¹⁰ may be moved by a predetermined distance in anx-direction and in a y-direction. To adjust the reproduction positionsof the holographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀, and L⁻¹⁰, the spatiallight modulator 120 may display the periodic diffraction pattern P asshown in FIG. 2, in addition to a hologram pattern including informationregarding a holographic image to be reproduced. A traveling direction ofthe incident light is thus deflected by the periodic diffraction patternP displayed by the spatial light modulator 120, and thus thereproduction positions of the holographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀,and L⁻¹⁰ are shifted from the lattice spots N0 and N1. When moving thereproduction positions of the holographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀,and L⁻¹⁰, a complex conjugate image denoted by * may be displayed at asymmetric position of the holographic image L₀₀, L₀₁, L⁻⁰¹, L₁₀, andL⁻¹⁰ based on the lattice spots N0 and N1.

Referring back to FIG. 1, the spatial filter 133 may be configured toblock a lattice spots N0 and N1 and a complex conjugate image and toallow only the plurality of holographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀, andL⁻¹⁰ to be transmitted therethrough. Thereby, the spatial filter 133 mayseparate the plurality of holographic images L₀₀, L₀₁, L⁻⁰¹, L₁₀, andL⁻¹⁰ generated by the hologram pattern displayed on the spatial lightmodulator 120 from the plurality of lattice spots N0 and N1 generated bythe physical structure of the spatial light modulator 120 and thecomplex conjugate image generated by the off-axis. In this way, a noiseimage produced due to the lattice spots N0 and N1 and the complexconjugate image will not be visible or will be less visible to theobserver. For example, the spatial filter 133 may include a plurality ofpinholes for allowing a plurality of holographic images to betransmitted therethrough. When the spatial filter 133 is positioned onthe focal plane of the first lens 131, positions of the plurality ofpinholes of the spatial filter 133 may coincide with the spot positionsof the plurality of holographic images.

However, when a blue light source, a green light source, and a red lightsource are used to realize a color holographic image, a position of aholographic image and a position of a lattice spot may be different foreach color. For example, FIG. 4 illustrates positions of a plurality ofholographic images for each color reproduced via an off-axis techniqueand a plurality of lattice spots for each color according to anexemplary embodiment. Referring to FIG. 4, each holographic imageincludes a blue holographic image, a green holographic image, and a redholographic image, and each lattice spot also includes a blue latticespot, a green lattice spot, and a red lattice spot. Circles indicated bydashed lines in FIG. 4 represent complex conjugate images.

The lattice spot N0 generated due to 0^(th) order diffraction by aphysical structure inside the spatial light modulator 120 is located atthe center of a focal plane of the first lens 131 and positions of theblue lattice spot, the green lattice spot, and the red lattice spot arevirtually the same. As a distance from the lattice spot N0 increases, adistance between the blue holographic image, the green holographicimage, and the red holographic image gradually increases, and a distancebetween the blue lattice spot, the green lattice spot, and the redlattice spot also gradually increases. For example, the holographicimage of each color and the lattice spots of each color are shifted awayfrom the lattice spot N0 in the order of blue, green, and red.

In the case of a holographic image generated by 0^(th) order diffractiondue to the hologram pattern nearest the lattice spot N0, althoughpositions of the blue holographic image B0, the green holographic imageG0 and the red holographic image R0 do not coincide with each other, thepositional differences thereamong are not large. Also, the blueholographic image B0, the green holographic image G0 and the redholographic image R0 generated due to 0^(th) order diffraction areclearly separated from the lattice spot N0. Therefore, the blueholographic image B0, the green holographic image G0 and the redholographic image R0 may be completely separated from the lattice spotsN0 and the complex conjugate images using only a single first pinhole H0formed as a circular opening.

Each of the plurality of lattice spots N1 generated due to 1^(st) orderdiffraction by the physical structure inside the spatial light modulator120 includes a blue lattice spot N1B, a green lattice spot N1G, and ared lattice spot N1R. A plurality of blue lattice spots N1B, a pluralityof green lattice spots N1G, and a plurality of red lattice spots N1R maybe symmetrically distributed with respect to the lattice spot N0. Theblue lattice spot N1B, the green lattice spot N1G, and the red latticespot N1R of a single lattice spot N1 partially overlap each other,through their centers are spaced apart from each other. Similarly, aplurality of blue holographic images B1, a plurality of greenholographic images G1 and a plurality of red holographic images R1generated due to 1st order diffraction by the hologram pattern may alsobe substantially symmetrically distributed with respect to the latticespot N0. The blue holographic image B1, the green holographic image G1and the red holographic image R1 belonging to one holographic imagepartially overlap each other, though their centers are spaced apart fromeach other.

Positional differences among the blue holographic image B1, the greenholographic image G1 and the red holographic image R1 generated due to1^(st) order diffraction are greater than the positional differencesamong the blue holographic image B0, the green holographic image G0, andthe red holographic image R0 generated due to 0^(th) order diffraction.Therefore, the blue holographic image B1, the green holographic image G1and the red holographic image R1 may not be clearly separated from theblue lattice spot N1B, the green lattice spot N1G, and the red latticespot N1R. For example, in FIG. 4, the green lattice spot N1G and the redlattice spot N1R are located very close to the blue holographic image B1and the green holographic image G1.

In this case, it may be difficult to completely separate the blueholographic image B1, the green holographic image G1 and the redholographic image R1 from the blue lattice spots N1B, the green latticespots N1G, and the red lattice spot N1R using only a second pinhole H1formed in the shape of an aperture. Therefore, the second pinhole H1 mayinclude a plurality of color filters for separating the greenholographic image G1 and the red holographic image R1 from the bluelattice spots N1B, the green lattice spots N1G, and the red lattice spotN1R. For example, referring to FIG. 4, the second pinhole H1 may includea first filter region SF1 centered on the blue holographic image B1, asecond filter region SF2 centered on the green holographic image G1, anda third filter region SF3 centered on the red holographic image R1. Thefirst filter region SF1 is larger than the blue holographic image B1 andmay have a common center with the blue holographic image B1. Likewise,the second filter region SF2 is larger than the green holographic imageG1 and may have a common center with the green holographic image G1, andthe third filter region SF3 is larger than the red holographic image R1and may have a common center with the holographic image R1.

FIG. 5 illustrates positions and shapes of the plurality of pinholes H0and H1 of the spatial filter 133 of the holographic display apparatus100 shown in FIG. 1 according to an exemplary embodiment. Referring toFIG. 5, the single first pinhole H0 is disposed at the center of thespatial filter 133. The first pinhole H0 may be a circular aperturepenetrating through the spatial filter 133 or a circular transparentwindow that transmits visible light. When the first pinhole H0 is theaperture, the first pinhole H0 may transmit light in all wavelengths.The first pinhole H0 may transmit a holographic image generated due to0th order diffraction in the spatial light modulator 120. To this end,the first pinhole H0 may be arranged to entirely encompass all spots ofthe blue holographic image B0, the green holographic image G0 and thered holographic image R0 in a focal plane of the first lens 131.

The plurality of second pinholes H1 are arranged around the firstpinhole H0. The second pinhole H1 may transmit a plurality of higherorder holographic images generated due to ±1^(st) order or higherdiffraction in the spatial light modulator 120. In order to separate theblue holographic image B1, the green holographic image G1 and the redholographic image R1 from the blue lattice spot NIB, the green latticespot N1G and the red lattice spot N1R, each of the second pinholes H1may include the first filter region SF1, the second filter region SF2,and the third filter region SF3. The plurality of first filter regionsSF1, the plurality of second filter regions SF2 and the plurality ofthird filter regions SF3 may be symmetrically disposed with respect tothe first pinhole H0. The first filter region SF1 is arranged toentirely encompass a spot of the blue holographic image B1 in the focalplane of the first lens 131, the second filter region SF2 is arranged toentirely encompass a spot of the green holographic image G1 in the focalplane of the first lens 131, and the third filter region SF3 is arrangedto entirely encompass a spot of the red holographic image R1 in thefocal plane of the first lens 131. A remaining part of the spatialfilter 133, excluding the first pinhole H0 and the second pinholes H1,may include an opaque material that does not transmit light.

In order to transmit only a holographic image of a desired color, aplurality of different color filters may be arranged in the first tothird filter regions SF1, SF2, and SF3. FIG. 6 illustrates anarrangement of a plurality of color filters disposed in the secondpinhole H1 of the spatial filter 133 of the holographic displayapparatus 100 shown in FIG. 1 according to an exemplary embodiment.Since the blue holographic image B1, the green holographic image G1 andthe red holographic image R1, belonging to one holographic image,overlap with each other, as shown in FIG. 6, the first to third filterregions SF1, SF2, and SF3 belonging to the single second pinhole H1 alsooverlap with each other. Accordingly, the first to third filter regionsSF1, SF2, and SF3 may be subdivided into a plurality of partial regions.For example, the second pinhole H1 may include a first region includingonly the first filter region SF1, a second region where the first filterregion SF1 and the second filter region SF2 overlap, a third regionincluding only the second filter region SF2, a fourth region where allthe first filter region SF1, the second filter region SF2 and the thirdfilter region SF3 overlap, a fifth region where the second filter regionSF2 and the filter region SF3 overlap, and a sixth region including onlythe sixth filter region SF6.

In this regard, the first region may correspond to a location of onlythe blue holographic image B1 on the spatial filter 133, and the secondregion may correspond to locations of the blue holographic image B1 andthe green holographic image G1 on the spatial filter 133. The thirdregion may correspond to a location of only the green holographic imageG1 on the spatial filter 133, the fourth region may correspond tolocations of all of the blue holographic image B1, the green holographicimage G1 and the red holographic image R1 on the spatial filter 133, thefifth region may correspond to locations of both of the greenholographic image G1 and the red holographic image R1 on the spatialfilter 133, and the sixth region may correspond to a location of onlythe red holographic image R1 on the spatial filter 133.

Accordingly, the second pinhole H1 may include a first color filter CF1arranged in the first region and transmitting the blue holographic imageB1, a second color filter CF2 arranged in the second region andtransmitting the blue holographic image B1 and the green holographicimage G1, a third color filter CF3 arranged in the third region andtransmitting the green holographic image G1, a fourth color filter CF4arranged in the fourth region and transmitting the blue holographicimage B1, the green holographic image G1 and the red holographic imageR1, a fifth color filter CF5 arranged in the fifth region andtransmitting the green holographic image G1 and the red holographicimage R1, and a sixth color filter CF6 arranged in the sixth region andtransmitting the red holographic image R1. For example, the fourth colorfilter CF4 may simply be an aperture or a transparent window thattransmits visible light. When the fourth color filter CF4 is theaperture, the fourth color filter CF4 may transmit light of allwavelengths.

Referring again to FIG. 5, the plurality of first filter regions SF1,the plurality of second filter regions SF2, and the plurality of thirdfilter regions SF3 may be symmetrically arranged with respect to thefirst pinhole H0. Since red light, having a long wavelength is refracteda comparatively little amount, and a blue light, having a shortwavelength, is refracted a comparatively large amount, the first filterregion SF1 corresponding to the blue holographic image B1 is arranged ata comparatively small distance to the first pinhole H0 and the thirdfilter region SF3 corresponding to the red holographic image R1 may bearranged at a comparatively long distance to the first pinhole H0.Therefore, from among the first through sixth color filters CF1, CF2,CF3, CF4, CF5, and CF6, the first color filter CF1 is arranged closestto the first pinhole H0. For example, a distance between the first colorfilter CF1 and the first pinhole H0 is smaller than a distance betweenthe sixth color filter CF6 and the first pinhole H0.

The holographic display apparatus 100 having the spatial filter 133having the above-described structure may effectively block not only thelattice spot N0 due to 0^(th) order diffraction but also the latticespots N1 due to 1^(st) order diffraction. Therefore, not only theholographic image formed by 0^(th) order diffraction but also theplurality of holographic images formed by 1^(st) or higher-orderdiffractions may be provided to an observer without noise. In this way,a space in which a user may observe the holographic image, that is, aviewing window is widened. Thus, the observer may observe theholographic image in a wider region.

The holographic display apparatus 100 shown in FIG. 1 has only onespatial filter 133, but is not limited thereto. FIG. 7 is aconfiguration diagram schematically showing a configuration of aholographic display apparatus 200 according to another exemplaryembodiment. Referring to FIG. 7, the holographic display apparatus 200may include three spatial filters 133B, 133G, and 133R disposed betweenthe first lens 131 and the second lens 132. For example, the firstspatial filter 133B separates a blue holographic image from a bluelattice spot and a blue complex conjugate image. The second spatialfilter 133G separates a green holographic image from a green latticespot and a green complex conjugate image, and the third spatial filter133B separates a red holographic image from a red lattice spot and a redcomplex conjugate image.

Since a focal length of the first lens 131 is different for differentwavelengths of light, the first to third spatial filters 133B, 133G and133R may be arranged at different positions on an optical axis betweenthe first lens 131 and the second lens 132. For example, the firstspatial filter 133B may be arranged at a blue light focal distance ofthe first lens 131, the second spatial filter 133G may be arranged at agreen light focal distance of the first lens 131, and the third spatialfilter 133R may be arranged at a red light focal distance of the firstlens 131. Accordingly, the first spatial filter 133B may be arrangedclosest to the first lens 131, and the second spatial filter 133G andthe third spatial filter 133R may be sequentially disposed, on theoptical path, after the first spatial filter 133B.

FIGS. 8A to 8C illustrate configurations of the first to third spatialfilters 133B, 133G and 133R of the holographic display apparatus 200shown in FIG. 7, respectively, according to an exemplary embodiment.Referring to FIGS. 8A to 8C, the first to third spatial filters 133B,133G and 133R may include band blocking filters arranged at positions ofa plurality of lattice spots. For example, the first spatial filter 133Bmay include a plurality of blue blocking filters 134B disposed atpositions corresponding to a plurality of blue lattice spots, in orderto block blue light and transmit green light and red light. The secondspatial filter 133G may include a plurality of green blocking filters134G disposed at positions corresponding to a plurality of green latticespots, in order to block the green light and transmit the blue light andthe red light. The third spatial filter 133R may include a plurality ofred blocking filters 134R disposed at positions corresponding to aplurality of red lattice spots, in order to block the red light andtransmit the blue light and the green light.

Remaining regions of the first to third spatial filters 133B, 133G, and133R in which the blue blocking filter 134B, the green blocking filter134G, and the red blocking filter 134R are not disposed may include amaterial transparent to visible light. In this way, a blue holographicimage may be transmitted through the first spatial filter 133B. Sincethe blue holographic image is transmitted through the green blockingfilter 134G or the red blocking filter 134R, the blue holographic imageis not blocked by the second spatial filter 133G or the third spatialfilter 133R. However, the blue lattice spots are incident on the blueblocking filter 134B of the first spatial filter 133B and thus blockedby the first spatial filter 133B. The green lattice spots are blocked bythe green blocking filter 134G of the second spatial filter 133G afterbeing transmitted through the first spatial filter 133B. Also, the redlattice spots are blocked by the red blocking filter 134R of the thirdspatial filter 133R after being transmitted through the first spatialfilter 133B and the second spatial filter 133G.

As shown in FIG. 4, the blue lattice spots N1B, the green lattice spotsN1G, and the red lattice spots N1R are sequentially spaced apart fromthe lattice spot NO, formed by 0^(th) order diffraction. Therefore,distances among the plurality of blue blocking filters 134B in the firstspatial filter 133B are relatively close. Distances among the pluralityof green blocking filters 134G in the second spatial filter 133G arelarger than the distances among the plurality of blue blocking filters134B. Also, distances among the plurality of red blocking filters 134Rin the third spatial filter 133R are larger than the distances among theplurality of green blocking filters 134G. Positions of the blue blockingfilters 134B, the green blocking filters 134G, and the red blockingfilters 134B, arranged at the centers of the first to third spatialfilters 133B, 133G, and 133R, respectively, and corresponding to thelattice spots N0 by 0^(th) order diffraction may coincide with eachother.

The blue blocking filter 134B, the green blocking filter 134G, and thered blocking filter 134R, shown in FIGS. 8A to 8C, may be large so as tocorrespond to not only lattice spots but also a plurality of complexconjugate images. Alternately, the blue blocking filter 134B, the greenblocking filter 134G, and the red blocking filter 134R corresponding tothe plurality of complex conjugate images may be separately formed.

FIGS. 9A to 9C illustrate different configurations of the first to thirdspatial filters 133B, 133G, and 133R of the holographic displayapparatus 200 shown in FIG. 7, respectively, according to an exemplaryembodiment. Referring to FIGS. 9A to 9C, the first to third spatialfilters 133B, 133G, and 133R may respectively include the blue blockingfilters 134B, the green blocking filters 134G, and the red blockingfilters 134R disposed at positions of a plurality of lattice spots, andmay also, respectively, include additional blue blocking filters 134B,green blocking filters 134G, and red blocking filters 134R disposed atpositions of a plurality of complex conjugate images. For example, thefirst spatial filter 133B may include the plurality of blue blockingfilters 134B disposed at positions corresponding to blue complexconjugate images, the second spatial filter 133G may include theplurality of green blocking filters 134G disposed at positionscorresponding to green complex conjugate images, and the third spatialfilter 133R may include the plurality of red blocking filters 134Rdisposed at positions corresponding to red complex conjugate images.

FIG. 10 is a schematic diagram showing a configuration of a holographicdisplay apparatus 300 according to another exemplary embodiment. In theholographic display apparatus 100 shown in FIG. 1, the spatial filter133 is shown as having a flat plate shape—i.e. a substantially planarshape. However, the focal plane on which the holographic images arefocused by the first lens 131 may not be perfectly flat but may have aparabolic shape. Therefore, the spatial filter 133 may be formed to havea shape corresponding with the focal plane of the first lens 131. Forexample, as shown in FIG. 10, the spatial filter 133 may have aparabolic shape. Then, the plurality of pinholes H0 and H1 of thespatial filter 133 may be accurately positioned on the focal plane ofthe first lens 131.

In the holographic display apparatuses 100, 200, and 300 describedabove, the spatial filters 133, 133B, 133G, and 133R are alltransmissive. However, it is also possible to configure a reflectivespatial filter. FIG. 11 is a schematic diagram showing a configurationof a holographic display apparatus 400 according to another exemplaryembodiment. Referring to FIG. 11, the holographic display apparatus 400may include a reflective spatial filter 135 disposed between the firstlens 131 and the second lens 132. The spatial filter 135 may removenoise by selectively reflecting only holographic images and transmittingor absorbing lattice spots and complex conjugate images. The opticalpath between the first lens 131 and the second lens 132 may be bent, forexample by about 90 degrees, by the spatial filter 135.

The spatial filter 135 may include a plurality of reflective surfaces toseparate a plurality of holographic images generated by a hologrampattern displayed on the spatial light modulator 120 from a plurality oflattice spots generated by a physical structure inside the spatial lightmodulator 120 and a complex conjugate image generated via an off-axis.Such a plurality of reflective surfaces may be formed in considerationof positions of a plurality of holographic images for each color andpositions of lattice spots for a plurality of colors shown in FIG. 4.For example, FIG. 12 exemplarily illustrates positions and shapes of aplurality of reflective surfaces M0 and M1 of the spatial filter 135 ofthe holographic display apparatus 400 shown in FIG. 11.

Referring to FIG. 12, the spatial filter 135 may include a firstreflective surface M0 reflecting a holographic image generated by 0^(th)order diffraction in the spatial light modulator 120 and a plurality ofsecond reflective surfaces M1 respectively reflecting a plurality ofhigher order holographic images generated by ±1^(st) or higher orders ofdiffraction. At the center of the spatial filter 135, one firstreflective surface M0 is disposed. The first reflective surface M0 maybe simply a circular plane mirror capable of reflecting light of allwavelengths. The first reflective surface M0 may reflect the holographicimage generated by 0^(th) order diffraction in the spatial lightmodulator 120. To this end, the first reflection surface M0 may bearranged in a position corresponding to all spots of the blueholographic image B0, the green holographic image G0 and the redholographic image R0 in a focal plane of the first lens 131.

The plurality of second reflective surfaces M1 are arranged around thefirst reflective surface M0. The second reflective surfaces M1 mayreflect the plurality of higher order holographic images generated by±1^(st) order or higher diffraction in the spatial light modulator 120.In order to separate the blue holographic images B1, the greenholographic images G1, and the red holographic images R1 from the bluelattice spots N1B, the green lattice spots N1G, and the red latticespots N1R, each of the second reflective surfaces M1 may include thefirst filter region SF1, the second filter region SF2, and the thirdfilter region SF3. The first filter regions SF1, the second filterregions SF2, and the third filter regions SF3 may be arrangedsymmetrically with respect to the first reflective surface M0. The firstfilter region SF1 is arranged to correspond to a spot of the blueholographic image B1 in the focal plane of the first lens 131, thesecond filter region SF2 is arranged to correspond to a spot of thegreen holographic image G1 in the focal plane of the first lens 131, andthe third filter region SF3 is arranged to correspond to a spot of thered holographic image R1 in the focal plane of the first lens 131. Theremaining part of the spatial filter 135, excluding the first reflectivesurface M0 and the second reflective surfaces M1, may include atransparent material which transmits light therethrough.

In order to reflect only a holographic image of a desired color, aplurality of different dichroic mirrors may be arranged in the first tothird filter regions SF1, SF2, and SF3. FIG. 13 illustrates anarrangement of a plurality of dichroic mirrors disposed on the secondreflective surface M1 in the spatial filter 135 of the holographicdisplay apparatus 400 shown in FIG. 11 according to an exemplaryembodiment. Since the blue holographic image B1, the green holographicimage G1, and the red holographic image R1, belonging to one singleholographic image overlap with each other, as shown in FIG. 13, thefirst through third filter regions SF1, SF2, and SF3, belonging to thesingle second reflective surface M1, also overlap with each other.Accordingly, the first to third filter regions SF1, SF2, and SF3 may besubdivided into a plurality of partial regions. For example, the secondreflective surface M1 may include a first region including only thefirst filter region SF1, a second region where the first filter regionSF1 and the second filter region SF2 overlap, a third region includingonly the second filter region SF2, a fourth region where all the firstfilter region SF1, the second filter region SF2 and the third filterregion SF3 overlap, a fifth region where the second filter region SF2and the filter region SF3 overlap, and a sixth region including only thesixth filter region SF6.

In this regard, the first region may correspond to a location of onlythe blue holographic image B1 on the spatial filter 135, and the secondregion may correspond to locations of the blue holographic image B1 andthe green holographic image G1 on the spatial filter 135. The thirdregion also may correspond to a location of only the green holographicimage G1 on the spatial filter 135, the fourth region may correspond tolocations of all of the blue holographic image B1, the green holographicimage G1 and the red holographic image R1 on the spatial filter 135, thefifth region may correspond to locations of both the green holographicimage G1 and the red holographic image R1 on the spatial filter 135, andthe sixth region may correspond to a location of only the redholographic image R1 on the spatial filter 135.

Accordingly, the second reflective surface M1 may include a firstdichroic mirror DM1 arranged in the first region, reflecting only bluelight and transmitting or absorbing light of other colors, a seconddichroic mirror DM2 arranged in the second region, reflecting only bluelight and green light and transmitting or absorbing light of othercolors, a third dichroic mirror DM3 arranged in the third region,reflecting only green light and transmitting or absorbing light of othercolors, a fourth dichroic mirror DM4 disposed in the fourth region andreflecting blue light, green light, and red light, a fifth dichroicmirror DM5 disposed in the fifth region, reflecting only green light andred light and transmitting or absorbing light of other colors, and asixth dichroic mirror DM6 disposed in the sixth region, reflecting onlyred light and transmitting or absorbing light of other colors. Forexample, the fourth dichroic mirror DM4 may be a simple mirror thatreflects light of all wavelengths, or may be a dichroic mirror thatreflects only visible light. Then, the first dichroic mirror DM1 mayreflect only the blue holographic image B1, the second dichroic mirrorDM2 may reflect only the blue holographic image B1 and the greenholographic image G1, the third dichroic mirror DM3 may reflect only thegreen holographic image G1, the fourth dichroic mirror DM4 may reflectthe blue holographic image B1, the green holographic image G1 and thered holographic image R1, the fifth dichroic mirror DM5 may reflect onlythe green holographic image G1 and the red holographic image R1, and thesixth dichroic mirror DM6 may reflect only the red holographic image R1.

Referring again to FIG. 12, the plurality of first filter regions SF1,the plurality of second filter regions SF2, and the plurality of thirdfilter regions SF3 may be symmetrically arranged with respect to thefirst reflective surface M0. For example, the first filter region SF1corresponding to the blue holographic image B1 may be disposedcomparatively closer to the first reflection surface M0, and the thirdfilter region SF3 corresponding to the red holographic image R1 may bedisposed comparatively farther from the first reflective surface M0.Therefore, among the first to sixth dichroic mirrors DM1, DM2, DM3, DM4,DM5 and DM6, the first dichroic mirror DM1 may be disposed closest tothe first reflective surface M0. For example, a distance between thefirst dichroic mirror DM1 and the first reflective surface M0 is smallerthan a distance between the sixth dichroic mirror DM6 and the firstreflective surface M0.

FIG. 14 is a schematic diagram showing a configuration of a holographicdisplay apparatus 500 according to another exemplary embodiment. Theholographic display apparatus 500 shown in FIG. 14 may include threespatial filters 135B, 135G, and 135R disposed between the first lens 131and the second lens 132. For example, the first spatial filter 135Bseparates a blue holographic image from a blue lattice spot and a bluecomplex conjugate image. The second spatial filter 135G separates agreen holographic image from a green lattice spot and a green complexconjugate image. The third spatial filter 135B separates a redholographic image from a red lattice spot and a red complex conjugateimage. To this end, the first spatial filter 135B may be disposed at ablue light focal distance of the first lens 131, the second spatialfilter 135G may be disposed at a green light focal distance of the firstlens 131, and the third spatial filter 135R may be disposed at a redlight focal distance of the first lens 131. Accordingly, the firstspatial filter 135B may be disposed closest to the first lens 131, andthe second spatial filter 135G and the third spatial filter 135R may besequentially disposed, on the optical path, after the first spatialfilter 135B.

FIGS. 15A to 15C illustrate configurations of the first to third spatialfilters 135B, 135G and 135R of the holographic display apparatus 500shown in FIG. 14, respectively, according to an exemplary embodiment.Referring to FIGS. 15A to 15C, the first to third spatial filters 135B,135G and 135R may include dichroic mirrors disposed at positions of aplurality of holographic images. For example, the first spatial filter135B may include a plurality of first dichroic mirrors 136B disposed atpositions corresponding to a plurality of blue holographic images B0 andB1, reflecting blue light, and transmitting green light and red light.The second spatial filter 135G may include a plurality of seconddichroic mirrors 136G disposed at positions corresponding to a pluralityof green holographic images G0 and G1, reflecting green light andtransmitting blue light and red light. The third spatial filter 135R mayinclude a plurality of third dichroic mirrors 136R disposed at positionscorresponding to a plurality of red holographic images R0 and R1,reflecting red light and transmitting blue light and green light.

Remaining regions of the first to third spatial filters 135B, 135G, and135R in which the first to third dichroic mirrors 136B, 136G, and 136Rare not disposed may include a material that is transparent to visiblelight. Accordingly, the blue holographic images B0 and B1 may bereflected by the first dichroic mirror 136B in the first spatial filter135B. However, since blue lattice spots and blue complex conjugateimages are not incident on the first dichroic mirror 136B, the bluelattice spots and blue complex conjugate images pass through the firstspatial filter 135B. The blue lattice spots and the blue complexconjugate images also pass through the second spatial filter 135G andthe third spatial filter 135R. The green holographic images G0 and G1may be reflected by the second dichroic mirror 136G in the secondspatial filter 135G after passing through the first spatial filter 135B.The red holographic images R0 and R1 may be reflected by the thirddichroic mirror 136R in the third spatial filter 135R after passingthrough the first spatial filter 135B and the second spatial filter135G. The green lattice spots, the green complex conjugate images, thered lattice spots, and the red complex conjugate images all pass throughthe first to third spatial filters 135B, 135G and 135R.

As shown in FIG. 4, the blue holographic image B1, the green holographicimage G1, and the red holographic image R1 are sequentially spaced awayfrom the lattice spot N0 by 0^(th) order diffraction. Therefore,distances among the plurality of first dichroic mirrors 136B in thefirst spatial filter 135B are relatively close. Distances among theplurality of second dichroic mirrors 136G in the second spatial filter135G are larger than the distances among the plurality of first dichroicmirrors 136B. Further, distances among the plurality of third dichroicmirrors 136R in the third spatial filter 135R are larger than thedistances among the plurality of second dichroic mirrors 136G. Positionsof the first to third dichroic mirrors 136B, 136G, and 136R arranged atthe approximate centers of the first through third spatial filters 135B,135G, and 135R and corresponding to the blue holographic image B0, thegreen holographic image G0, and the red holographic image R0 by 0^(th)order diffraction respectively are almost the same but not identical.

While holographic display apparatuses for providing an expanded viewingwindow, described above, have been shown and described in connectionwith the exemplary embodiments illustrated in the drawings, it will beunderstood by those of ordinary skill in the art that variousmodifications and equivalent embodiments may be made therefrom.Therefore, the disclosed exemplary embodiments should be considered inan illustrative sense rather than a restrictive sense. The range of theembodiments will be in the appended claims, and all of the differencesin the equivalent range thereof should be understood to be included inthe embodiments.

What is claimed is:
 1. A holographic display apparatus comprising: alight source; a spatial light modulator comprising a plurality of pixelsarranged in a lattice, wherein the spatial light modulator is configuredto modulate light incident thereon from the light source and output aplurality of holographic images, and wherein a physical structure of thelattice outputs a plurality of lattice spots; and a spatial filterconfigured to direct the plurality of holographic images toward a viewerand to block the plurality of lattice spots or to direct the pluralityof lattice spots away from the viewer, wherein each of the plurality ofholographic images comprises a first color image and a second colorimage, wherein each of the plurality of lattice spots comprises a firstcolor lattice spot and a second color lattice spot, and wherein thespatial filter is configured to separate the first color image and thesecond color image from the first color lattice spot and the secondcolor lattice spot such that the first color image and the second colorimage are directed toward the viewer and the first color lattice spotand the second color lattice spot are blocked or directed away from theviewer.
 2. The holographic display apparatus of claim 1, wherein thespatial filter comprises a first pinhole transmitting a holographicimage generated by a 0th order diffraction in the spatial lightmodulator, and a plurality of second pinholes respectively transmittinga plurality of high order holographic images generated by a ±1st orhigher order diffraction in the spatial light modulator.
 3. Theholographic display apparatus of claim 2, wherein the first pinhole isconfigured to transmit the first color image and the second color imageof the holographic image generated by the 0th order diffraction.
 4. Theholographic display apparatus of claim 2, wherein each of the pluralityof second pinholes comprises the plurality of color filters.
 5. Theholographic display apparatus of claim 4, wherein each of the pluralityof second pinholes comprises a first region on which the first colorimage is incident, a second region on which the first color image andthe second color image are incident, and a third region on which thesecond color image is incident.
 6. The holographic display apparatus ofclaim 5, wherein the plurality of color filters comprises: a first colorfilter disposed in the first region and configured to transmit the firstcolor image; a second color filter disposed in the second region andconfigured to transmit the first color image and the second color image;and a third color filter disposed in the third region and configured totransmit the second color image.
 7. The holographic display apparatus ofclaim 6, wherein a distance between the first color filter and the firstpinhole is less than a distance between the third color filter and thefirst pinhole.
 8. The holographic display apparatus of claim 1, whereinthe spatial filter comprises a first reflective surface reflecting aholographic image generated by a 0th order diffraction in the spatiallight modulator and a plurality of second reflective surfacesrespectively reflecting a plurality of high order holographic imagesgenerated by a ±1st order or higher diffraction in the spatial lightmodulator.
 9. The holographic display apparatus of claim 8, wherein thefirst reflective surface is configured to reflect the first color imageand the second color image of the holographic image generated by the 0thorder diffraction.
 10. The holographic display apparatus of claim 8,wherein each of the plurality of second reflective surfaces comprisesthe plurality of dichroic mirrors.
 11. The holographic display apparatusof claim 10, wherein each of the plurality of second reflective surfacescomprises a first region on which the first color image is incident, asecond region on which the first color image and the second color imageare incident, and a third region on which the second color image isincident.
 12. The holographic display apparatus of claim 11, wherein theplurality of dichroic mirrors comprises: a first dichroic mirrordisposed in the first region and configured to reflect the first colorimage; a second dichroic mirror disposed in the second region andconfigured to reflect the first color image and the second color image;and a third dichroic mirror disposed in the third region and configuredto reflect the second color image.
 13. The holographic display apparatusof claim 1, further comprising: a first lens disposed between thespatial light modulator and the spatial filter; and a second lensconfigured to focus the plurality of holographic images separated by thespatial filter.
 14. The holographic display apparatus of claim 13,wherein the spatial filter comprises: a first spatial filter disposed ata position at which the first color image is focused by the first lens;and a second spatial filter disposed at a position at which the secondcolor image is focused by the first lens.
 15. The holographic displayapparatus of claim 14, wherein the first spatial filter comprises aplurality of first color blocking filters respectively disposed atpositions corresponding to the first color lattice spots and configuredto block light of a first color and to transmit light of a differentcolor, and wherein the second spatial filter comprises a plurality ofsecond color blocking filters respectively disposed at positionscorresponding to the second color lattice spots and configured to blocklight of a second color and to transmit light of a different color. 16.The holographic display apparatus of claim 15, wherein remaining regionsof the first spatial filter and the second spatial filter in which theplurality of first color blocking filters and the plurality of secondcolor blocking filters are not disposed comprise a transparent material.17. The holographic display apparatus of claim 15, wherein the firstspatial filter comprises a plurality of additional first color blockingfilters respectively disposed at positions corresponding to complexconjugate images of the first color image, and wherein the secondspatial filter comprises a plurality of additional second color blockingfilters respectively disposed at positions corresponding to complexconjugate images of the second color image.
 18. The holographic displayapparatus of claim 14, wherein the first spatial filter comprises aplurality of first dichroic mirrors respectively disposed at positionscorresponding to the first color images and configured to reflect lightof the first color and to transmit light of the second color, whereinthe second spatial filter comprises a plurality of second dichroicmirrors respectively disposed at positions corresponding to the secondcolor images and configured to reflect light of the second color and totransmit light of the first color.
 19. The holographic display apparatusof claim 18, wherein remaining regions of the first spatial filter andthe second spatial filter in which the plurality of first dichroicmirrors and the plurality of second dichroic mirrors are not disposedcomprise a transparent material.
 20. The holographic display apparatusof claim 1, wherein the spatial filter has a hemispheric or paraboloidshape.